wdiff rfc6764.original rfc6764.txt

Network Working Group
Internet Engineering Task Force (IETF) C. Daboo
Internet-Draft
Request for Comments: 6764 Apple Inc.
Updates: 4791,CardDAV-RFC-to-be September 16, 2010
(if approved)
Intended status: 4791, 6352 October 2012
Category: Standards Track
Expires: March 20, 2011
ISSN: 2070-1721

Locating CalDAV Services for Calendaring Extensions to WebDAV (CalDAV) and CardDAV services
draft-daboo-srv-caldav-10
vCard Extensions to WebDAV (CardDAV)

Abstract

This specification describes how DNS SRV records, DNS TXT records records,
and well-known URIs can be used together or separately to locate
Calendaring
CalDAV (Calendaring Extensions to WebDAV (CalDAV) Web Distributed Authoring and
Versioning (WebDAV)) or vCard CardDAV (vCard Extensions to
WebDAV (CardDAV) WebDAV)
services.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on March 20, 2011.
http://www.rfc-editor.org/info/rfc6764.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 ....................................................2
2. Conventions Used in This Document . . . . . . . . . . . . . . 4 ...............................3
3. CalDAV SRV Service Labels . . . . . . . . . . . . . . . . . . 4 .......................................3
4. CalDAV and CardDAV Service TXT Records . . . . . . . . . . . . 4 ..........................4
5. CalDAV and CardDAV Service Well-Known URI . . . . . . . . . . 5 .......................4
5.1. Example: well-known Well-Known URI redirects Redirects to actual context
path . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Actual
"Context Path" .............................................5
6. Client "Bootstrapping" Procedures . . . . . . . . . . . . . . 5 ...............................5
7. Guidance for Service Providers . . . . . . . . . . . . . . . . 8 ..................................8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 .........................................8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 .............................................9
9.1. Well-Known URI Registrations ...............................9
9.1.1. caldav Well-Known URI Registration . . . . . . . . . . . . 10
9.2. ..................9
9.1.2. carddav Well-Known URI Registration . . . . . . . . . . . 10
9.3. SRV ................10
9.2. Service Name Registrations ................................10
9.2.1. caldav Service Name Registration ...................10
9.2.2. caldavs Service Name Registration ..................10
9.2.3. carddav Service Name Registration ..................11
9.2.4. carddavs Service Label Name Registration . . . . . . . . . . . . . . 10 .................11
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 ...............................................11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ....................................................12
11.1. Normative References . . . . . . . . . . . . . . . . . . . 10 .....................................12
11.2. Informative References . . . . . . . . . . . . . . . . . . 12
Appendix A. Change History (to be removed prior to
publication as an RFC) . . . . . . . . . . . . . . . 13 ...................................13

1. Introduction

[RFC4791] defines the CalDAV calendar access protocol, based on HTTP
[RFC2616], for accessing calendar data stored on a server. CalDAV
clients need to be able to discover appropriate CalDAV servers within
their local area network and at other domains, e.g., to minimize the
need for end users to know specific details such as the fully
qualified domain name (FQDN) and port number for their servers.

[I-D.ietf-vcarddav-carddav]

[RFC6352] defines the CardDAV address book access protocol based on
HTTP [RFC2616], for accessing contact data stored on a server. As
with CalDAV, clients also need to be able to discover CardDAV
servers.

[RFC2782] defines a DNS-based service discovery protocol that has
been widely adopted as a means of locating particular services within
a local area network and beyond, using DNS SRV Resource Records
(RRs). This has been enhanced to provide additional service meta-
data by use of DNS TXT Resource Records RRs as per
[I-D.cheshire-dnsext-dns-sd]. [RFC6763].

This specification defines new SRV service types for the CalDAV
protocol,
protocol and gives an example of how clients can use this together
with other protocol features to enable simple client configuration.
SRV service types for CardDAV are already defined in Section 11 of
[I-D.ietf-vcarddav-carddav].
[RFC6352].

Another issue with CalDAV or CardDAV service discovery is that the
service might not be located at the "root" URI of the HTTP server
hosting it. Thus Thus, a client needs to be able to determine the
complete path component of the Request-URI to use in HTTP requests:
the "context path". For example, if CalDAV is implemented as a
"servlet" in a web server "container", the servlet "context path"
might be "/caldav/". So the URI for the CalDAV service would be,
e.g., "http://caldav.example.com/caldav/" rather than
"http://caldav.example.com/". SRV RRs by themselves only provide a an
FQDN and port number for the service, not a path. Since the client
"bootstrapping" process requires initial access to the "context path"
of the service, there needs to be a simple way for clients to also
discover what that path is.

This specification makes use of the "well known "well-known URI" feature
[RFC5785] of HTTP servers to provide a well known well-known URI for CalDAV or
CardDAV services that clients can make use of. use. The well known well-known URI will point
to a resource on the server that is simply a "stub" resource that
provides a redirect to the actual "context path" resource
representing the service endpoint.

2. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. CalDAV SRV Service Labels

This specification adds two SRV service labels for use with CalDAV:

_caldav: Identifies a CalDAV server that uses HTTP without transport
layer security ([RFC2818]).
Transport Layer Security (TLS) [RFC2818].

_caldavs: Identifies a CalDAV server that uses HTTP with transport
layer security ([RFC2818]). TLS
[RFC2818].

Clients MUST honor "Priority" Priority and "Weight" Weight values in the SRV RRs, as
described by [RFC2782].

Example: service record for server without transport layer security TLS

_caldav._tcp SRV 0 1 80 calendar.example.com.

Example: service record for server with transport layer security TLS

_caldavs._tcp SRV 0 1 443 calendar.example.com.

4. CalDAV and CardDAV Service TXT Records

When SRV RRs are used to advertise CalDAV and CardDAV services, it is
also convenient to be able to specify a "context path" in the DNS to
be retrieved at the same time. To enable that, this specification
uses a TXT RR that follows the syntax defined in Section 6 of
[I-D.cheshire-dnsext-dns-sd]
[RFC6763] and defines a "path" key for use in that record. The value
of the key MUST be the actual "context path" to the corresponding
service on the server.

A site might provide TXT records in addition to SRV records for each
service. When present, clients MUST use the "path" value as the
"context path" for the service in HTTP requests. When not present,
clients use the ".well-known" URI approach described next.

Example: text record for service with transport layer security TLS

_caldavs._tcp TXT path=/caldav

5. CalDAV and CardDAV Service Well-Known URI

Two ".well-known" URIs are registered by this specification for
CalDAV and CardDAV services, "caldav" and "carddav" respectively (see
Section 9). These URIs point to a resource that the client can use
as the initial "context path" for the service they are trying to
connect to. The server MUST redirect HTTP requests for that resource
to the actual "context path" using one of the available mechanisms
provided by HTTP (e.g., using a 301, 303, or 307 response). Clients
MUST handle HTTP redirects on the ".well-known" URI. Servers MUST
NOT locate the actual CalDAV or CardDAV service endpoint at the
".well-known" URI as per Section 1.1 of [RFC5785].

Servers SHOULD set an appropriate Cache-Control header value (as per
Section 14.9 of [RFC2616]) in the redirect response to ensure caching
occurs or does not occur as needed, needed or as required by the type of
response generated. For example, if it is anticipated that the
location of the redirect might change over time, then a "no-cache"
value would be used.

To facilitate "context path's" paths" that might differ from user to user,
the server MAY require authentication when a client tries to access
the ".well-known" URI (i.e., the server would return a 401 status
response to the unauthenticated request from the client, then return
the redirect response only after a successful authentication by the
client).

5.1. Example: well-known Well-Known URI redirects Redirects to actual context path Actual "Context Path"

A CalDAV server has a "context path" that is "/servlet/caldav". The
client will use "/.well-known/caldav" as the path for its
"bootstrapping" process after it has first found the FQDN and port
number via an SRV lookup or via manual entry of information by the
user
user, from which the client can parse suitable information from. information. When the
client makes an HTTP request against "/.well-known/caldav", the
server would issue an HTTP redirect response with a Location response
header using the path "/servlet/caldav". The client would then
"follow" this redirect to the new resource and continue making HTTP
requests there to complete its "bootstrapping" process.

6. Client "Bootstrapping" Procedures

This section describes a procedure that CalDAV or CardDAV clients
SHOULD use to do their initial configuration based on minimal user
input. The goal is to determine an http: or https: URI that
describes the full path to the user's principal-URL [RFC3744].

1. Processing user input:

* For a CalDAV server:

+ Minimal input from a user would consist of a calendar user
address and a password. A calendar user address is defined
by iCalendar [RFC5545] to be a URI [RFC3986]. Provided a
user identifier and a domain name can be extracted from the
URI, this simple "bootstrap" "bootstrapping" configuration can be done.

+ If the calendar user address is a "mailto:" [RFC2368] [RFC6068] URI,
the "mailbox" portion of the URI is examined examined, and the
"local-part" and "domain" portions are extracted.

+ If the calendar user address is an "http:" [RFC2616] or
"https:" [RFC2818] URI, the "userinfo" and "host" portion
of the URI [RFC3986] is extracted.

* For a CardDAV server:

+ Minimal input from a user would consist of their email
address [RFC5322] for the domain where the CardDAV service
is hosted, and a password. The "mailbox" portion of the
email address is examined examined, and the "local-part" and
"domain" portions are extracted.

2. Determination of service FQDN and port number:

* An SRV lookup for _caldavs._tcp (for CalDAV) or _carddavs._tcp
(for CardDAV) is done with the extracted "domain" as the
service domain.

* If no result is found, the client can try _caldav._tcp (for
CalDAV) or _carddav._tcp (for CardDAV) provided non-SSL non-TLS
connections are appropriate.

* If an SRV record is returned, the client extracts the target
FQDN and port number. In the case of If multiple SRV records are returned,
the client MUST use the priority Priority and weight Weight fields in the
record to determine which one to pick (as per [RFC2782]).

* If an SRV record is not found, the client will need to prompt
the user to enter the FQDN and port number information
directly,
directly or use some other heuristic, for example example, using the
extracted "domain" as the FQDN and default HTTPS or HTTP port
numbers. In this situation situation, clients MUST first attempt an
HTTP connection with transport layer security. TLS.

3. Determination of initial "context path":

* When an SRV lookup is done and a valid SRV record returned,
the client MUST also query for a corresponding TXT record and
check for the presence of a "path" key in its response. If
present, the value of the "path" key is used for the initial
"context path".

* When an initial "context path" has not been determined from a
TXT record, the initial "context path" is taken to be "/.well-
known/caldav" (for CalDAV) or "/.well-known/carddav" (for
CardDAV).

* If the initial "context path" derived from a TXT record
generates HTTP errors when targeted by requests, the client
SHOULD repeat its bootstrap "bootstrapping" procedure using the
appropriate ".well-known" URI instead.

4. Determination of user identifier:

* The client will need to make authenticated HTTP requests to
the service. Typically Typically, a "user identifier" is required for
some form of user/password authentication. When a user
identifier is required, clients MUST first use the "mailbox"
portion of the calendar user address provided by the user in
the case of a "mailto:" address, and address and, if that results in an
authentication failure, SHOULD fall back to using the "local-
part" extracted from the "mailto:" address. For an "http:" or
"https:" calendar user address, the "userinfo" portion is used
as the user identifier for authentication. This is in line
with the guidance outlined in Section 7. If these user
identifiers result in authentication failure, the client
SHOULD prompt the user for a valid identifier.

5. Connecting to the service:

* Subsequent to configuration, the client will make HTTP
requests to the service. When using "_caldavs" or "_carddavs"
services, a transport layer security TLS negotiation is done immediately upon
connection. The client MUST do certificate verification using
the procedure outlined in Section 4 6 of
[I-D.saintandre-tls-server-id-check] [RFC6125] in regard to
verification with an SRV RR as the starting point.

* The client does a "PROPFIND" [RFC4918] request with the
request URI set to the initial "context path". The body of
the request SHOULD include the DAV:current-user-principal
[RFC5397] property as one of the properties to return. Note
that clients MUST properly handle HTTP redirect responses for
the request. The server will use the HTTP authentication
procedure outlined in [RFC2617] or use some other appropriate
authentication schemes to authenticate the user.

* If the server returns a 404 Not Found ("Not Found") HTTP status response
to the request on the initial "context path", clients MAY try
repeating the request on the "root" URI "/" or prompt the user
for a suitable path.

* If the DAV:current-user-principal property is returned on the
request, the client uses that value for the principal-URL of
the authenticated user. With that, it can execute a
"PROPFIND" request on the principal-URL and discover
additional properties for configuration (e.g., calendar or
address book "home" collections).

* If the DAV:current-user-principal property is not returned,
then the client will need to request the principal-URL path
from the user in order to continue with configuration.

Once a successful account discovery step has been done, clients
SHOULD cache the service details that were successfully used (user
identity, principal-URL with full scheme/host/port details), details) and re-
use reuse
those when connecting again at a later time.

If a subsequent connection attempt fails, or authentication fails
persistently, clients SHOULD re-try retry the SRV lookup and account
discovery to "refresh" the cached data.

7. Guidance for Service Providers

Service providers wanting to offer CalDAV or CardDAV services that
can be configured by clients using SRV records need to follow certain
procedures to ensure proper operation.

o CalDAV or CardDAV servers SHOULD be configured to allow
authentication with calendar user addresses (just taking the
"mailbox" portion of any "mailto:" URI) or email addresses
respectively, or with "user identifiers" extracted from them. In
the former case, the addresses MUST NOT conflict with other forms
of a permitted user login name. In the latter case, the extracted
"user identifiers" need to be unique across the server and MUST
NOT conflict with any login name on the server.

o Servers MUST force authentication for "PROPFIND" requests that
retrieve the DAV:current-user-principal property to ensure that
the value of the DAV:current-user-principal property returned
corresponds to the principal-URL of the user making the request.

o If the service provider uses transport layer security, TLS, the service provider MUST ensure
a certificate is installed that can be verified by clients using
the procedure outlined in Section 4 6 of
[I-D.saintandre-tls-server-id-check] [RFC6125] in regard to
verification with an SRV RR as the starting point. In particular,
certificates SHOULD include SRV-ID and DNS-ID identifiers as
appropriate, as described in Section 8.

o Install Service providers should install the appropriate SRV records for
the offered services.
Optionally services and optionally include TXT records.

8. Security Considerations

Clients that support transport layer security TLS as defined by [RFC2818] SHOULD try the
"_caldavs" or "_carddavs" services first before trying the "_caldav"
or "_carddav" services respectively. If a user has explicitly
requested a connection with transport layer security, TLS, the client MUST NOT use any service
information returned for the "_caldav" or "_carddav" services.
Clients MUST follow the
certificate verification certificate-verification process specified in
[I-D.saintandre-tls-server-id-check].
[RFC6125].

A malicious attacker with access to the DNS server data, or that is
able to get spoofed answers cached in a recursive resolver, can
potentially cause clients to connect to any server chosen by the
attacker. In the absence of a secure DNS option, clients SHOULD
check that the target FQDN returned in the SRV record matches the
original service domain that was queried. If the target FQDN is not
in the queried domain, clients SHOULD verify with the user that the
SRV target FQDN is suitable for use before executing any connections
to the host. Alternatively, if transport layer security TLS is being used for the service,
clients MUST use the procedure outlined in Section 4 6 of
[I-D.saintandre-tls-server-id-check] [RFC6125] to
verify the service.

Implementations of TLS [RFC5246], used as When the basis for transport
layer security target FQDN does not match the original
service domain that was queried, clients MUST check the SRV-ID
identifier in the server's certificate. If the FQDN does match,
clients MUST check any SRV-ID identifiers in the server's certificate
or, if no SRV-ID identifiers are present, MUST check the DNS-ID
identifiers in the server's certificate.

Implementations of TLS [RFC5246], used as the basis for TLS
([RFC2818]), typically support multiple versions of the protocol as
well as the older Secure SSL (Secure Sockets Layer (SSL) Layer) protocol. Because of
known security vulnerabilities, clients and servers MUST NOT request,
offer, or use SSL 2.0. See Appendix E.2 of [RFC5246] for further
details.

9. IANA Considerations

9.1. Well-Known URI Registrations

This document defines two ".well-known" URIs using the registration
procedure and template from Section 5.1 of [RFC5785].

9.1.

9.1.1. caldav Well-Known URI Registration

URI suffix: caldav

Change controller: IETF. IETF

Specification document(s): This RFC. RFC

Related information: See also [RFC4791].

9.2.

9.1.2. carddav Well-Known URI Registration

URI suffix: carddav

Change controller: IETF. IETF

Specification document(s): This RFC. RFC

Related information: See also [I-D.ietf-vcarddav-carddav].

9.3. SRV [RFC6352].

9.2. Service Label Name Registrations

This document registers four new service names as per [RFC6335]. Two
are defined in this document, and two are defined in [RFC6352],
Section 11.

9.2.1. caldav Service Name Registration

Service labels have been registered according Name: caldav

Transport Protocol(s): TCP

Assignee: IESG <iesg@ietf.org>

Contact: IETF Chair <chair@ietf.org>

Description: Calendaring Extensions to
<http://www.dns-sd.org/ServiceTypes.html> [1] and will be
incorporated into IANA once a new registry WebDAV (CalDAV) - non-TLS

Reference: [RFC6764]

Assignment Note: This is available there. an extension of the http service. Defined
TXT keys: path=<context path>

9.2.2. caldavs Service Name Registration

Service Name: caldavs

Transport Protocol(s): TCP

Assignee: IESG <iesg@ietf.org>

Contact: IETF Chair <chair@ietf.org>

Description: Calendaring Extensions to WebDAV (CalDAV) - over TLS

Reference: [RFC6764]
Assignment Note: This is an extension of the https service. Defined
TXT keys: path=<context path>

9.2.3. carddav Service Name Registration

Service Name: carddav

Transport Protocol(s): TCP

Assignee: IESG <iesg@ietf.org>

Contact: IETF Chair <chair@ietf.org>

Description: vCard Extensions to WebDAV (CardDAV) - non-TLS

Reference: [RFC6352]

Assignment Note: This is an extension of the http service. Defined
TXT keys: path=<context path>

9.2.4. carddavs Service Name Registration

Service Name: carddavs

Transport Protocol(s): TCP

Assignee: IESG <iesg@ietf.org>

Contact: IETF Chair <chair@ietf.org>

Description: vCard Extensions to WebDAV (CardDAV) - over TLS

Reference: [RFC6352]

Assignment Note: This is an extension of the https service. Defined
TXT keys: path=<context path>

10. Acknowledgments

This specification was suggested by discussion that took place within
the Calendaring and Scheduling Consortium's CalDAV Technical
Committee. The author thanks the following for their contributions:
Stuart Cheshire, Bernard Desruisseaux, Eran Hammer-Lahav, Helge Hess,
Arnaud Quillaud, Wilfredo Sanchez, and Joe Touch.

11. References

11.1. Normative References

[I-D.cheshire-dnsext-dns-sd] Cheshire, S. and M. Krochmal,
"DNS-Based Service Discovery",
draft-cheshire-dnsext-dns-sd-06
(work in progress), March 2010.

[I-D.ietf-vcarddav-carddav] Daboo, C., "vCard Extensions to
WebDAV (CardDAV)",
draft-ietf-vcarddav-carddav-10
(work in progress),
November 2009.

[I-D.saintandre-tls-server-id-check] Saint-Andre, P. and J. Hodges,
"Representation and
Verification of Domain-Based
Application Service Identity in
Certificates Used with
Transport Layer Security", draf
t-saintandre-tls-server-id-
check-09 (work in progress),
August 2010.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2368] Hoffman, P., Masinter, L., and
J. Zawinski, "The mailto URL
scheme", RFC 2368, July 1998.

[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.

[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.

[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

[RFC3744] Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
Distributed Authoring and Versioning (WebDAV)
Access Control Protocol", RFC 3744, May 2004.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.

[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
March 2007.

[RFC4918] Dusseault, L., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918, June 2007.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.

[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.

[RFC5397] Sanchez, W. and C. Daboo, "WebDAV Current Principal
Extension", RFC 5397, December 2008.

[RFC5785] Nottingham, M. and E. Hammer-
Lahav, Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
April 2010.

11.2. Informative References

[RFC5545] Desruisseaux, B., "Internet
Calendaring

[RFC6068] Duerst, M., Masinter, L., and Scheduling Core
Object Specification
(iCalendar)", J. Zawinski, "The 'mailto'
URI Scheme", RFC 5545,
September 2009.

URIs

[1] <http://www.dns-sd.org/ServiceTypes.html>

Appendix A. Change History (to be removed prior to publication as an
RFC)

Changes in -09:

1. IESG Review: minor editorial changes.

2. GenART Review: minor editorial changes.

3. GenART Review: "guideline" -> "procedure".

4. GenART Review: "port" -> "port number".

5. GenART Review: added definition of "context path".

6. GenART Review: clarified OPTIONAL nature of suggested client
procedure.

7. GenART Review: clarified that TXT lookup is an additional query.

8. IESG Review: now allow any HTTP redirect response, not just 301.

9. IESG Review: added text on cache interaction with redirect.

Changes in -10:

1. AD Review: make client procedure a SHOULD.

Changes in -08:

1. Clarify that email address is a valid input in Section 7 for
CardDAV.

2. Clarified aspects of DAV:current-user-principal handling for
servers.

3. Added additional text to indicate TXT being used in abstract and
introduction.

Changes in -07:

1. Add password to required minimal user input

2. Section 3 -> Section 4 of server-id check draft.

Changes in -06:

1. Last call comments: Revised title, abstract 6068, October 2010.

[RFC6125] Saint-Andre, P. and text to indicate
that SRV J. Hodges, "Representation and .well-known can be done separately.

2. Revised IANA section to use dns-sd registry for now.

3. Added optional TXT RR with path key for service context path
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the DNS

4. Re-organized client bootstrap to take account Context of TXT and to call-
out the different "phases" involved via a numbered list.

Changes in -05:

1. AD Review: Added "Updates" for 4791 Transport Layer
Security (TLS)", RFC 6125, March 2011.

[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and CardDAV.

2. AD Review: Changed SHOULD to MUST S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for honoring priority and
weight.

3. AD Review: Added additional reference to 3986 when talking about
userinfo/host portions the Management of the URI.

4. AD Review: Changed section reference for tls-server-id-check
draft.

5. AD Review: Changed should to SHOULD when describing PROPFIND
request Service Name and made 5397 normative.

6. AD Review: Made 3744 and 5322 normative references.

7. AD Review: Added IANA SRV registration request.

Changes in -04:

1. Added addition text
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, August 2011.

[RFC6352] Daboo, C., "CardDAV: vCard Extensions to client guidelines indicating that clients
cache the discovery details Web Distributed
Authoring and can re-do discovery if
connections later fail.

2. Changed principal-URI to principal-URL.

Changes in -03:

1. Updated to Versioning (WebDAV)", RFC 5785 reference.

2. Added SSL v2 restriction from srv-email document added after IESG
review.

3. Tweaked client/server guidelines to better match HTTP challenge/
response authentication mechanism.

Changes in -02:

1. Re-organized introduction.

2. Brought terminology into line with srv-email document which has
been through last call.

3. Brought security section into line with srv-email document which
has been through last call.

Changes in -01:

1. Added discovery of CardDAV service.

2. Now makes use of well-known URIs for the service "context path".

3. Updated to 6352, August 2011.

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 5545 reference.

4. Added reference to certificate verification spec. 6763, September 2012.

11.2. Informative References

[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling
Core Object Specification (iCalendar)", RFC 5545,
September 2009.

Author's Address

Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA

EMail: cyrus@daboo.name
URI: http://www.apple.com/